diff --git a/.editorconfig b/.editorconfig
index 0b172c41ab..a0e1655de2 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -233,6 +233,9 @@ dotnet_diagnostic.CA1816.severity = warning # not default, increased severity to
 # CA1018: Mark attributes with AttributeUsageAttribute
 dotnet_diagnostic.CA1018.severity = warning # not default, increased severity to ensure it is applied
 
+# CA1051: Do not declare visible instance fields
+dotnet_diagnostic.CA1051.severity = warning # not default, increased severity to ensure it is applied
+
 #### C# Coding Conventions ####
 
 # var preferences
diff --git a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
index 88227019f1..522881f531 100644
--- a/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
+++ b/src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
@@ -44,9 +44,11 @@ public class DesignModeClient : IDesignModeClient
     private readonly IEnvironment _platformEnvironment;
     private readonly TestSessionMessageLogger _testSessionMessageLogger;
     private readonly object _lockObject = new();
-    [System.Diagnostics.CodeAnalysis.SuppressMessage("Style", "IDE1006:Naming Styles", Justification = "Part of the public API.")]
+    [SuppressMessage("Style", "IDE1006:Naming Styles", Justification = "Part of the public API.")]
+    [SuppressMessage("Design", "CA1051:Do not declare visible instance fields", Justification = "Part of the public API")]
     protected Action<Message>? onCustomTestHostLaunchAckReceived;
-    [System.Diagnostics.CodeAnalysis.SuppressMessage("Style", "IDE1006:Naming Styles", Justification = "Part of the public API.")]
+    [SuppressMessage("Style", "IDE1006:Naming Styles", Justification = "Part of the public API.")]
+    [SuppressMessage("Design", "CA1051:Do not declare visible instance fields", Justification = "Part of the public API")]
     protected Action<Message>? onAttachDebuggerAckRecieved;
 
     /// <summary>
diff --git a/src/Microsoft.TestPlatform.Extensions.HtmlLogger/ObjectModel/TestRunDetails.cs b/src/Microsoft.TestPlatform.Extensions.HtmlLogger/ObjectModel/TestRunDetails.cs
index 12f841ed5f..12af69e5b2 100644
--- a/src/Microsoft.TestPlatform.Extensions.HtmlLogger/ObjectModel/TestRunDetails.cs
+++ b/src/Microsoft.TestPlatform.Extensions.HtmlLogger/ObjectModel/TestRunDetails.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.Serialization;
 
 namespace Microsoft.VisualStudio.TestPlatform.Extensions.HtmlLogger.ObjectModel;
@@ -10,6 +11,7 @@ namespace Microsoft.VisualStudio.TestPlatform.Extensions.HtmlLogger.ObjectModel;
 /// It stores the all relevant information of the test run.
 /// </summary>
 [DataContract]
+[SuppressMessage("Design", "CA1051:Do not declare visible instance fields", Justification = "Part of the public API")]
 public sealed class TestRunDetails
 {
     /// <summary>
diff --git a/test/.editorconfig b/test/.editorconfig
index 2be7bb24d6..0197e0b09d 100644
--- a/test/.editorconfig
+++ b/test/.editorconfig
@@ -15,6 +15,9 @@ dotnet_diagnostic.IDE0060.severity = warning
 # CA1018: Mark attributes with AttributeUsageAttribute
 dotnet_diagnostic.CA1018.severity = warning
 
+# CA1051: Do not declare visible instance fields
+dotnet_diagnostic.CA1051.severity = silent # Disabled on tests as it does not matter
+
 #### C# Coding Conventions ####
 
 #### .NET Formatting Rules ####
diff --git a/test/Microsoft.TestPlatform.TestUtilities/TestableTestPluginCache.cs b/test/Microsoft.TestPlatform.TestUtilities/TestableTestPluginCache.cs
index e8855920d4..98097a2972 100644
--- a/test/Microsoft.TestPlatform.TestUtilities/TestableTestPluginCache.cs
+++ b/test/Microsoft.TestPlatform.TestUtilities/TestableTestPluginCache.cs
@@ -11,7 +11,7 @@ namespace Microsoft.TestPlatform.TestUtilities;
 
 public class TestableTestPluginCache : TestPluginCache
 {
-    public Action? Action;
+    public Action? Action { get; set; }
 
     public TestableTestPluginCache(List<string> extensionsPath)
     {